<!doctype html>
<title>CSS Masking: An invalid mask reference generates a transparent black mask</title>
<div style="width: 100px; height: 100px; background-color: green">
  <svg mask="url(#nonexistent)" style="-webkit-mask: url(#nonexistent)">
    <rect width="100" height="100" fill="red"/>
  </svg>
</div>
